Nozzle for a pyrolytic coating and deposition process



E. T. MYsKowsKl NOZZLE FOR A PYROLIITIC'COATING AND DEPOSITION PROCESS Filed April 1. 1968 Aug. 18N, 1970 United States Patent O 3,524,590 NOZZLE FOR A PYROLYTIC COATING AND DEPOSITION PROCESS Edwin T. Myskowsk, Wayne, Pa., assignor to General Electric Company, a corporation of New York Filed Apr. 1, 1968, Ser. No. 717,506 Int. Cl. B05b 7/06 U.S. Cl. Z39-424.5 5 Claims ABSTRACT OF THE DISCLOSURE In accordance with the present invention, two coaxially flowing iluids are made to interact to produce an extremely stable, coherent single stream which is essentially a vortex in cross section. The inherent coherency and stability of this stream make it very effective for the controlled delivery of reacting gases into mandrels with small enclosed angles used in processes such as the production of sharp-tipped pyrolytic graphite members.

INTRODUCTION This invention pertains to a method and apparatus for forming sharp tipped members by gas decomposition processes. More specifically it pertains to a-nozzle useful in such methods and apparatus.

BACKGROUND OF THE INVENTION Attempts to form sharp tipped members, such as certain space reentry nose cones, by gas decomposition-deposition processes have heretofore been frustrated by the diiculty in obtaining non-turbulent ow of the reactant gas into the apexl of a female conical mandrel with a small enclosed angle. In all known prior art methods and apparatus, interference with this gas flow by turbulence near the apex and the reverse ow of gas away from the apex inhibits deposition in the apex. Therefore conformance to mandrel shape is poor in the area of the mandrel apex and the tip of the article formed contains voids and discontinuities.

It is therefore an object of this invention to provide a nozzle for producing a smooth, stable, slow flowing elongated uid stream of controlled diameter, extending for some distance away from the nozzle, and capable of penetrating a deep cavity, such as the small enclosed angle in a female conical mandrel.

BRIEF DESCRIPTION OF THE INVENTION These and other objects are met, in accordance with the present invention, by apparatus including a female conical mandrel with a highly acute enclosed angle and means for heating the mandrel to the decomposition temperature of the coating gas. The apparatus also includes, as a critical element therein, a nozzle for producing a smooth flow of coating gas into the tip of the mandrel apex. This nozzle comprises a central duct, an annular duct surrounding the central duct and coaxial therewith, a central duct terminus, an annular duct terminus axially adjacent the central duct terminus, means for causing separate uid streams to emanate, in preselected volumetric ratios, from the nozzle duct termini and means for causing a slight perturbation, near the central duct terminus, in the uid stream emanating from the annular duct terminus. This perturbation causes the stream emanating from the annular duct to assume a vortical path about a core stream, i.e. the uid stream emanating from the central duct terminus. Together the two streams set up a stable, generally vortical, flow pattern projecting for a substantial distance away from the nozzle.

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DETAILED DESCRIPTION OF THE INVENTION While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the present invention, this invention may be better understood from the following description taken in conjunction with the following drawings in which:

FIG. 1 is a cross sectional view of the nozzle comprising the preferred form of the present invention;

FIG. 2 is a partially cutaway isometric view of the nozzle shown in FIG. l; and

FIG. 3 is an illustration, partially schematic and partially in cross section, of apparatus for making sharp tipped conical members by a gas decomposition-deposition process using a nozzle such as that shown in FIGS. 1 and 2.

Referring more specifically to FIGS. l and 2, wherein like numerals correspond to like elements, there is shown a nozzle 10 comprised of a central duct 12, an annular duct 14 surrounding central duct 12 and coaxial therewith, a central duct terminus 16, an annular duct terminus 18, a porous material 20, such as open pore ceramic foam, disposed in annular duct 14, ad a closure member 22, with a plurality of openings 24 therethrough, in annular duct 14 near central duct terminus 16. Nozzle 10 also includes a fluid stream inlet 26 for central duct 12, a fluid stream inlet 28 for annular duct 14, a main support member 29 and duct housing 31. In the embodiment of the invention shown, the outer wall 30 of annular duct 14 comprises a water cooling jacket for nozzle 10, which facilitates its use in high temperature environments. Water ducts 33 serve as inlet and outlet for the water cooling jacket.

The generation and projection of a stable, vortical uid ow pattern |by nozzle 10 requires volumetrically proportioned fluid ow rates in central duct 12 and annular duct 14. This may be obtained, for example, by a valve and flow meter in each of the inlet lines 26 and 28, if a capability for variable proportioning is desired, or appropriately sized orifices placed at the point of separation of a single uid stream entering inlet lines 26 and 28.

The purpose of porous material 20 is to distribute any uid stream in annular duct 14 throughout the annular cross section thereof. This function may equally well be accomplished by mainifolding inlet line 28 into several openings distributed around annular duct 14, by appropriately placed baffles, by lengthening annular duct 14 or by various combinations' of the means described.

The function of closure member 22 with openings 24 therein is to cause a slight perturbation in the fluid stream in annular duct 14 near central duct terminus 16. This function may equally well be performed =by a screen or baffle member disposed across annular duct 14 near central duct terminus 16.

It will be noticed in FIG. l, that annular duct 14 projects for a distance beyond central duct terminus 16'. While this projection of annular duct 14 is not critical, it enhances the desired fluid flow patterns emanating from nozzle 10, described hereinafter, by providing limited confinement of the fluid stream in annular duct 14 at the point where the uid stream emanating from central duct terminus 16 rst contacts the uid stream in annular duct 14. In this embodiment, in which outer wall 30 of annular duct 14, comprises a water cooling jacket, the extension of wall 30 beyond central duct terminus 16 also serves t0 better control the temperature in nozzle 10.

Nozzle 10 may be used to produce a stable, smooth and highly useful uid flow pattern which extends for some distance away from duct termini 16 and 18. This flow pattern consists of a core stream emanating from central duct terminus 16 and an annular stream, i.e. a stream with components parallel to the core stream and tangential to the periphery thereof, following the periphery of the core stream. This vortical current is apparently generated in the fluid stream in annular duct 14 Iby virtue of the combined effects of the core stream and eddy currents caused by flow perturbation means 24 in the annular stream near the central duct terminus 16. The core and annular uid streams appear to combine or converge only after they have travelled some distance away from the nozzle. Because of these characteristics, the nozzle disclosed herein may be used to convey a deposition gas into the very riarrow tip of a female conical mandrel for making sharp tipped members with apex angles on the order of 4-10. This nozzle may also be used for bringing dissimilar fluids into contact at some point remote from the delivery means therefor.

Obviously, the fluid flow pattern produced by nozzles of the type described above Will |be disturbed by interfering uid ows, such as stray wind currents, etc. Therefore, these nozzles are usually used in hooded enclosures or closed chambers.

Looking now to FIG. 3, there is shown nozzle incorporated in an apparatus for making sharp tipped conical members by a gas decomposition process. -More specically, this set-up also includes a female conical mandrel 32 having an apex 34, with an enclosed angle on the order of 4 to 10 degrees, and an inductive heating coil 36 with heater core member or susceptor 38 for uniformly heating mandrel 32 to the decomposition temperature of the coating gas. The mandrel supporting skirt 40 includes gas escape ports 42. An insulated enclosure 44, vented to a vacuum pump, houses nozzle 10, mandrel 32 and the inductive heating unit. A mandrel and nozzle mounting member 46, a nozzle holding clamp 48 and a nozzle sealing member 50 completes the apparatus shown in FIG. 3.

In the apparatus shown in FIG. 3, a slow, smooth fluid flow pattern, created by nozzle 10, flows into the mandrel apex 34, and is reversed at the mandrel apex without turbulence or interference. It then ows smoothly back along the wall of mandrel 32 and escapes through ports 42.

Generally it has been found that a vortically stabilized stream may be produced with a nozzle of the type described above, having a major diameter in the annular duct of 3%: inch, a central duct terminus diameter in the range 0.060 to 0.125 inch, total dow rates for the two streams ranging from 6 to l2 standard cubic feet per hour and volumetric flow rate ratios between annular duct and central duct streams of 21/2-4 to 1.

A nozzle such as that shown in FIG. l, with a 0.205 inch inner diameter central duct, terminated with a 0.069 inch orifice and a 3A inch inner diameter in the outer wall of the annular duct, has been used to demonstrate the highly stabilized, extended fluid stream patterns producible in accordance with the present invention. Lubricating oil fog droplets, carried in nitrogen at 70 P. and 4.5 pounds per square inch, were passed through the central duct at 2 standard cubic feet per hour while nitrogen, also at 70 and 4.5 pounds per square inch, was passed through the annular duct at 6 standard cubic feet per hour. As these gases emanated from the respective duct termini they entered a space, open to the atmosphere ibut protected from stray air currents'. The oil fog stream emanating from the central duct lwas stabilized by the nitrogen gas emanating from the annular duct and travelled the full length of a four foot long glass tube without significantly increasing its diameter. When the oil fog was passed through the annular duct at 6 standard cubic feet per hour and nitrogen emanated from the central duct at 2 standard cubic feet per hour, the resultant stream consisted of a clear core surrounded by the oil fog. This stabilized stream acted in a manner identical to the oil fog core stream and demonstrated the dilusionless interaction of the two coaxial streams.

When similar vortex stabilized streams with the same ow rates, ow rate ratios, etc., were injected into a rv duced pressure chamber such as a glass bell jar maintained at 10 torr absolute pressure, the reduced pressure environment appeared to further stabilize the flow. This improved stabilization was evidenced by a reduction of the diameter of the central core stream from 0.069 inch at the central duct terminus to about 0.030 inch three inches downstream. This reduced diameter of the stream permits greater control of the flow and permits penetration of smaller and deeper openings in the mandrels used for pyrolytic deposition processes.

In a demonstration of other aspects of the present invention, mass flow rates and volumetric ratios established in bell jar studies were used to deposit pyrolytic graphite, from a hydrocarbon gas, on a mandrel for graphite deposition in a furnace at 4000 F. and 8 torr absolute pressure. The bell jar studies indicated that 2 standard cubic feet per hour methane through the 0.06-9 inch central duct terminus and 6 standard cubic feet per hour methane through the annular duct would produce maximum stability of the stream with optimum return flow along the mandrel. These ow rates were then used to produce uniform, high quality, defect-free, deposits of pyrolytic graphite on female conical mandrels the apexes of which have enclosed angles less than 10. The mandrel apexes,

in the demonstration runs, were about 8 inches from the nozzle. When removed from the mandrel, the pyrolytic graphite deposits comprised a sharp-tipped conical mem ber, suitable, for example, for use as a small re-entry vehicle nose cone.

While the present invention has been described with reference to particular embodiments thereof for purposes of clarity and convenience, it should be understood that numerous modifications may be made by those skilled in the art without departing from the inventions true spirit and scope. Therefore the appended claims are intended to cover all such equivalent variations as come Within the true spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A nozzle for producing a stable, vortical fluid flow consisting of a core stream and an annular stream following the periphery of said core stream comprising a central duct, a central duct terminus, an annular duct surrounding said central duct and coaxial therewith, an annular duct terminus axially adjacent said central duct terminus, means for causing separate uid streams to flow through each of said ducts and to emanate from the respective duct termini, means for proportioning the volumetric ow rates of the fluid streams in the respective ducts such that the flow rate in the annular duct is from 21/2 to 4 times that in the central duct, means in the annular duct for causing the fluid stream in the annular duct to be evenly distributed throughout the annular cross section thereof and means for causing the iluid stream emanating from said annular duct to assume a vortical path about the fluid stream emanating from said central duct terminus.

2. A nozzle, as recited in claim 1, wherein said means for causing the even distribution of the stream in the annular duct comprises a mass of non-reactive porous material in said annular duct near the terminus thereof.

3. A nozzle, as recited in claim 1, wherein said means for causing the fluid stream emanating from said annular duct to assume a vortical path comprises a thin planar member disposed across said annular duct with a multiwall of said annular duct extends axially for a short distane beyond said central duct terminus.

References Cited UNITED STATES PATENTS 6 FOREIGN PATENTS 8/ 1907 Great Britain. 3/1943 Italy.

5 LLOYD L. KING, Primary Examiner U.S. Cl. X.R. 

